The present invention relates to a failover method of a computing system including a server which is booted from an external disk device.
In general, a computing system such as a server is configured in such a manner that the OS (Operating System) installed in a built-in disk is booted and then business work is performed on the OS. Examples of methods for enhancing reliability of such a server include one method in which a backup server having the same configuration is provided and the main server is switched over to the backup server when the main server fails. With this method, however, since it is not possible to take over data concerning the business work stored in the disk, it is necessary to execute the work processing in progress over again. Further, another method is to transfer data concerning work among a plurality of servers via a network and, to take over the whole data concerning the business work in case either one server fails. Use of such a method enables the backup server to continue work that is in progress. Although the former method has an advantage that it is applicable to all sorts of business program, it cannot take over business work. On the other hand, the latter method has an advantage that it can take over business work in progress, but it is required to arrange that a business application should have a mechanism that transfers business data to a backup server, which restricts application of the method to all business applications.
Examples of methods for solving the disadvantages of the above-described two methods for enhancing reliability include a method, as stated in U.S. Patent Application Publication Nos. 2005/0060607A1 and 2003/0188115A1, wherein booting of the OS is accelerated by booting the OS from a snapshot that is acquired in advance. Here, the term “snapshot” means information including memory status where the OS or a business program is in operation. By storing a snapshot in a disk or the like and by booting a server by using the snapshot, it is possible to resume the OS or the business program at high-speed. Thus, by using the snapshot and booting a server at high-speed when the server fails, it is possible to recover the server while ensuring the active status of the OS or the business program.
Although the above-stated conventional arts can recover the server along while ensuring the active status of the OS or the business program by booting the server by using a snapshot at a high speed when the server fails, the failover function does not work depending on a snapshot to be used. For example, when a server acquired a snapshot during a time period when the sever is in failure, even if the server is recovered by using the snapshot and the OS or the business program is resumed, there will be a problem in reliability since the sever is booted in failed and unstable memory status. Therefore, the fact in which status of a server a snapshot was acquired constitutes a very important issue and, to ensure failover function, a snapshot that is acquired under normal operating status becomes mandatory.